Through a series of thought experiments, Richard Foley (Intellectual Trust in Oneself and Others) develops a concept of rationality as “a matter of making oneself invulnerable to intellectual self-criticism to the extent possible, of living up to one’s own deepest intellectual convictions and standards.” Rationality thus “requires one to have opinions and to use faculties, methods, and practices that are capable of withstanding one’s own, most severe critical scrutiny” (39).
One effect of this definition of rationality is to show that it's possible to be rational and deeply wrong at the same time: “one can be rational in this sense even if one is a brain-in-a-vat whose opinions are massively unreliable, and likewise one can be rational even if one’s opinions, methods, and assumptions are massively at odds with those of one’s community, era, and tradition” (39).
Foley wants to distinguish between a failure of rationality and an intellectual flaw: “Being fixed on an opinion is an intellectual failing but not necessarily a failure of rationality, and the same is true of many, other intellectual shortcomings. Imagine individuals who think that simple direct observation is a less reliable way of getting information about the environment than, say, relying on dreams. Most of us are convinced that perception generally provides us with reliable information about the world. Our beliefs typically extend well beyond what we can directly perceive, but direct observational beliefs, we think, provide a kind of tether even for these beliefs. They constrain our other beliefs and, we trust, prevent them from being utter fabrications. By contrast, the above individuals think, and we can stipulate that on reflection they would continue to think, that perception is a less reliable way of getting information about the world than relying on their dreams. If their opinions about the external world somehow manage to be in accord with these convictions, these opinions might conceivably pass the above test of epistemic rationality” (41).
This position also enables Foley to make sense of intellectual iconoclasts, who tear apart the “sacred canopy” under which everyone else huddles. In Foley's view, they need not be irrational in doing so: “it is possible, given the above account, for one’s opinions to be seriously at odds with one’s contemporaries and tradition and yet still be capable of withstanding one’s own most severe critical scrutiny and, hence, still be rational” (43).
This seems to entail an every-man-for-himself rationality. But Foley is right: We need somehow to account for the reality of iconoclasm, which makes it obvious that rationality is not entirely bound to social conditions or a tradition of inquiry.